\documentclass{article}
\usepackage{pgfplots}

\pgfplotsset{
	compat=1.9,
  minor tick num=1,
  samples=2,
  xlabel=xlabel,
  ylabel=ylabel,
}

\begin{document}
\begin{tikzpicture}
	\begin{axis}[
		axis lines=center,
		axis y line shift=-2,
		axis x line shift=100,
		grid=major]
	\addplot {30*x};
	\end{axis}
\end{tikzpicture}

\vspace{1cm}

\begin{tikzpicture}
	\begin{axis}[
		axis lines=left,
		axis y line shift=-2,
		axis x line shift=-100,
		y dir=reverse,
		clip limits=false,
		xmin=-5,
		ymax=100,
		grid=major]
	\addplot {30*x};
	\end{axis}
\end{tikzpicture}
\end{document}
